Hybrid vehicles are adapted for using both an engine and a motor generator being running power sources to drive wheels. Hybrid vehicles are equipped with a battery that has a large capacity for services including electric power supply and charge to the motor generator. The battery is charged by the motor generator that generates electricity when operated for regeneration or when driven by the engine, so electric power is available from the battery for operating the motor generator to drive the drive wheels. The battery deteriorates under overcharge conditions. It therefore is desirable to suppress the deterioration, with an extended service life.
There have been proposals made for hybrid vehicles (for instance, refer to the PTL1 below), including operations of an engine in order to employ, not only torque of a motor generator, but also torque of the engine for a drive of vehicle in a travel needing a large drive force at a low-vehicle speed, such as when starting a hill-climbing movement.